I can usually do this as well. I think it just takes getting into a regular schedule. For quite a few years I wasn't able to do it because I'd be pretty hammered almost every day. Now that I'm not drinking, I often beat my alarm by a few minutes or so.

That's awesome, I myself do not have that ability. Not even close. If I don't set an alarm I will sleep hours beyond what I am supposed to. Thats cool that you can do that. Do you sleep deeply? Get the REM?

Nope, because I can do it without a clock in the room. Good theory though. I've met one other person who could do this btw, I'm just wondering how uncommon it is. It has to do with my circadian rhythm, which is basically your body's internal clock.

I end up doing this when I forget to set my alarm the night before. Not only this, but I also wake up and am instantly aware of my surroundings before someone even gets to my room when they are going to come in.

Out of curiosity, do you wear a watch? Because I used to wear one years ago, and I remember it had a profound effect on my sense of time. I'm not sure if it was because I checked the time more often and got used to the feeling of time passing, or just subconsciously noticed it because it was in my field of vision frequently, or what. People would ask me the time because I had a watch and I would tell them without looking, which would be met with skepticism until showed them I wasn't wrong. One day the battery died, and I started using my phone to tell time until I got around to getting a replacement, and I just never did. Since then my sense of time has almost completely degraded. I think that the fact it was an analog watch also helped, as I would always think of the time as the hands on the clock face which move at a constant rate.